Publications
295 results found
Ungureanu B, Makwana M, Craster R, et al., 2020, Localising symmetry protected edge waves via the topological rainbow effect, Publisher: arXiv
We combine two different fields, topological physics and metamaterials to design a topological metasurface tocontrol and redirect elastic waves. We strategically design a two-dimensional crystalline perforated elastic platethat hosts symmetry-induced topological edge states. By concurrently allowing the elastic substrate to spatiallyvary in depth, we are able to convert the incident slow wave into a series of robust modes, with differing envelopemodulations. This adiabatic transition localises the incoming energy into a concentrated region where it can thenbe damped or extracted. For larger transitions, different behaviour is observed; the incoming energy propagatesalong the interface before being partitioned into two disparate chiral beams. This “topological rainbow” effectleverages two main concepts, namely the quantum valley-Hall effect and the rainbow effect usually associatedwith electromagnetic metamaterials. The topological rainbow effect transcends specific physical systems, hence,the phenomena we describe can be transposed to other wave physics. Due to the directional tunability of theelastic energy by geometry our results have far-reaching implications for applications such as switches, filtersand energy-harvesters.
Ji Q, Chen X, Liang J, et al., 2020, Non-Singular Homogeneous Polyhedral Heat Cloak and Its Realization, ES Energy and Environment, Vol: 7, Pages: 29-39, ISSN: 2578-0646
As most arbitrarily shaped cloaks can be approximated by polyhedra and further divided into a series of tetrahedra, we propose in this paper a linear mapping approach to design cloaks with tetrahedron shapes (i. e. tetrahedral cloaks). Homogeneous material properties of the cloak are straightforwardly obtained from coordinates of typical points. Consequently, most arbitrarily shaped thermal cloaks can be designed using homogeneous anisotropic materials only. We construct two polyhedral cloaks and show numerically that they successfully thermally conceal objects after a certain lapse of time. We then demonstrate that cloaks with curved boundaries can also be obtained using our approach. It is further shown how geometrical parameters affect the material properties and cloaking performances. One can flexibly tune the cloaking performances based on practical requirements and material availabilities. We analyze effectiveness of a polygonal cloak composed of an alternation of homogeneous isotropic layers, and note that cloaking deteriorates at short times. We finally sketch an approach to realize 3D homogenized thermal metamaterials.
Farhat M, Chen PY, Bagci H, et al., 2020, Scattering theory and cancellation of gravity-flexural waves of floating plates, Physical Review B, Vol: 101, ISSN: 2469-9950
We combine theories of scattering for linearized water waves and flexural waves in thin elastic plates to characterize and achieve control of water wave scattering using floating plates. This requires manipulating a sixth-order partial differential equation with appropriate boundary conditions of the velocity potential. Making use of multipole expansions, we reduce the scattering problem to a linear algebraic system. The response of a floating plate in the quasistatic limit simplifies, considering a distinct behavior for water and flexural waves. Unlike for similar studies in electromagnetics and acoustics, scattering of gravity-flexural waves results in a nonvanishing scattering cross-section in the zero-frequency limit, dominated by its zeroth-order multipole. Potential applications lie in floating structures manipulating ocean water waves.
Brule S, Enoch S, Guenneau S, 2020, Emergence of seismic metamaterials: Current state and future perspectives, PHYSICS LETTERS A, Vol: 384, ISSN: 0375-9601
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- Citations: 72
Achaoui Y, Diatta A, Kadic M, et al., 2020, Cloaking in-plane elastic waves with swiss rolls, Materials, Vol: 13
We propose a design of cylindrical cloak for coupled in-plane shear waves consisting of concentric layers of sub-wavelength resonant stress-free inclusions shaped as Swiss rolls. The scaling factor between inclusions' sizes is according to Pendry's transform. Unlike the hitherto known situations, the present geometric transform starts from a Willis medium and further assumes that displacement fields u in original medium and u' in transformed medium remain unaffected (u' = u). This breaks the minor symmetries of the rank-4 and rank-3 tensors in theWillis equation that describe the transformed effective medium. We achieve some cloaking for a shear polarized source at specific, resonant sub-wavelength, frequencies, when it is located in close proximity to a clamped obstacle surrounded by the structured cloak. The structured medium approximating the effective medium allows for strong Willis coupling, notwithstanding potential chiral elastic effects, and thus mitigates roles ofWillis and Cosserat media in the achieved elastodynamic cloaking.
Kadic M, Wegener M, Nicolet A, et al., 2020, Elastodynamic behavior of mechanical cloaks designed by direct lattice transformations, Wave Motion, Vol: 92, ISSN: 0165-2125
Steering waves in elastic solids is more demanding than steering waves in electromagnetism or acoustics. As a result, designing material distributions which are the counterpart of optical invisibility cloaks in elasticity poses a major challenge. Waves of all polarizations should be guided around an obstacle to emerge on the downstream side as though no obstacle were there. Recently, we have introduced the direct-lattice-transformation approach. This simple and explicit construction procedure led to extremely good cloaking results in the static case. Here, we transfer this approach to the dynamic case, i.e., to elastic waves or phonons. We demonstrate broadband reduction of scattering, with best suppressions exceeding a factor of five when using cubic coordinate transformations instead of linear ones. To reliably and quantitatively test these cloaks efficiency, we use an effective-medium approach.
Pomot L, Payan C, Remillieux M, et al., 2020, Acoustic cloaking: Geometric transform, homogenization and a genetic algorithm, Wave Motion, Vol: 92, ISSN: 0165-2125
A general process is proposed to experimentally design anisotropic inhomogeneous metamaterials obtained through a change of coordinates in the Helmholtz equation. The method is applied to the case of a cylindrical transformation that allows cloaking to be performed. To approximate such complex metamaterials we apply results of the theory of homogenization and combine them with a genetic algorithm. To illustrate the power of our approach, we design three types of cloaks composed of isotropic concentric layers structured with three types of perforations: curved rectangles, split rings and crosses. These cloaks have parameters compatible with existing technology and they mimic the behavior of the transformed material. Numerical simulations have been performed to qualitatively and quantitatively study the cloaking efficiency of these metamaterials.
Brûlé S, Enoch S, Guenneau S, 2019, Role of nanophotonics in the birth of seismic megastructures, Nanophotonics, Vol: 8, Pages: 1591-1605
The discovery of photonic crystals 30 years ago in conjunction with research advances in plasmonics and metamaterials, has inspired the concept of decameter scale metasurfaces, coined seismic metamaterials for an enhanced control of surface (Love and Rayleigh) and bulk (shear and pressure) elastodynamic waves. These powerful mathematical tools of coordinate transforms, effective medium and Floquet-Bloch theories which have revolutionized nanophotonics, can be translated in the language of civil engineering and geophysics. Experiments on seismic metamaterials made of buried elements in the soil demonstrate that the fore mentioned tools make a possible novel description of complex phenomena of soil-structure interaction during a seismic disturbance. But the concepts are already moving to more futuristic concepts and the same notions developed for structured soils are now used to examine the effects of buildings viewed as above surface resonators in megastructures such as metacities. But this perspective of future should not make us forget the heritage of the ancient peoples. Indeed, we finally point out the striking similarity between an invisible cloak design and the architecture of some ancient megastructures as the antique Gallo-Roman theaters and amphitheatres.
Brule S, Enoch S, Guenneau S, 2019, Role of nanophotonics in the birth of seismic megastructures, NANOPHOTONICS, Vol: 8, Pages: 1591-1605, ISSN: 2192-8606
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- Citations: 8
Ungureanu B, Guenneau S, Achaoui Y, et al., 2019, The influence of building interactions on seismic and elastic body waves, EPJ Applied Metamaterials, Vol: 6, Pages: 1-12, ISSN: 2272-2394
We outline some recent research advances on the control of elastic waves in thin and thick plates, that have occurred since the large scale experiment [S. Brûlé, Phys. Rev. Lett. 112, 133901 (2014)] that demonstrated significant interaction of surface seismic waves with holes structuring sedimentary soils at the meter scale. We further investigate the seismic wave trajectories of compressional body waves in soils structured with buildings. A significant substitution of soils by inclusions, acting as foundations, raises the question of the effective dynamic properties of these structured soils. Buildings, in the case of perfect elastic conditions for both soil and buildings, are shown to interact and strongly influence elastic body waves; such site-city seismic interactions were pointed out in [Guéguen et al., Bull. Seismol. Soc. Am. 92, 794–811 (2002)], and we investigate a variety of scenarios to illustrate the variety of behaviours possible.
Cherkaev E, Guenneau S, Hutridurga H, et al., 2019, Quasiperiodic composites: Multiscale reiterated homogenization, Pages: X086-X088
With recent technological advances, quasiperiodic and aperiodic materials present a novel class of metamaterials that possess very unusual, extraordinary properties such as superconductivity, unusual mechanical properties and diffraction patterns, extremely low thermal conductivity, etc. As all these properties critically depend on the microgeometry of the media, the methods that allow characterizing the effective properties of such materials are of paramount importance. In this paper, we analyze the effective properties of a class of multiscale composites consisting of periodic and quasiperiodic phases appearing at different scales. We derive homogenized equations for the effective behavior of the composite and discover a variety of new effects which could have interesting applications in the control of wave and diffusion phenomena.
Huidobro PA, Galiffi E, Guenneau S, et al., 2019, Fresnel drag in space-time-modulated metamaterials, Publisher: arXiv
A moving medium drags light along with it as measured by Fizeau and explained by Einstein's theory of special relativity. Here we show that the same effect can be obtained in a situation where there is no physical motion of the medium. Modulations of both the permittivity and permeability, phased in space and time in the form of travelling waves, are the basis of our model. Space-time metamaterials are represented by effective bianisotropic parameters, which can in turn be mapped to a moving homogeneous medium. Hence these metamaterials mimic a relativistic effect without the need for any actual material motion. We discuss how both the permittivity and permeability need to be modulated in order to achieve these effects, and we present an equivalent transmission line model.
Kadic M, Diatta A, Frenzel T, et al., 2019, Static chiral Willis continuum mechanics for three-dimensional chiral mechanical metamaterials, Physical Review B, Vol: 99, ISSN: 2469-9950
Recent static experiments on twist effects in chiral three-dimensional mechanical metamaterials have been discussed in the context of micropolar Eringen continuum mechanics, which is a generalization of linear Cauchy elasticity. For cubic symmetry, Eringen elasticity comprises nine additional parameters with respect to linear Cauchy elasticity, of which three directly influence chiral effects. Here, we discuss the behavior of the static case of an alternative generalization of linear Cauchy elasticity, the Willis equations. We show that in the homogeneous static cubic case, only one additional parameter with respect to linear Cauchy elasticity results, which directly influences chiral effects. We show that the static Willis equations qualitatively describe the experimentally observed chiral twist effects, too. We connect the behavior to a characteristic length scale.
Makwana M, Craster R, Guenneau S, 2019, Topological beam-splitting in photonic crystals, Optics Express, Vol: 27, Pages: 16088-16102, ISSN: 1094-4087
We create a passive wave splitter, created purely by geometry, to engineer three-way beam splitting in electromagnetism in transverse electric and magnetic polarisation. We do so by considering arrangements of Indium Phosphide dielectric pillars in air, in particular we place several inclusions within a cell that is then extended periodically upon a square lattice. Hexagonal lattice structures are more commonly used in topological valleytronics but, as we discuss, three-way splitting is only possible using a square, or rectangular, lattice. To achieve splitting and transport around a sharp bend we use accidental, and not symmetry-induced, Dirac cones. Within each cell pillars are either arranged around a triangle or square; we demonstrate the mechanism of splitting and why it does not occur for one of the cases. The theory is developed and full scattering simulations demonstrate the effectiveness of the proposed designs.
Makwana M, Craster R, Guenneau S, 2019, Topological beam-splitting in photonic crystals, Publisher: OPTICAL SOC AMER
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- Citations: 43
Cherkaev E, Guenneau S, Wellander N, 2019, Forward and inverse homogenization of the electromagnetic properties of a quasiperiodic composite
The paper deals with forward and inverse homogenization of Maxwell's equations with a geometry on a microscopic scale given by a quasiperiodic distribution of piece-wise constant components defined by the use of a mapping R: realsn → realsm, m > n, and a periodic unit cell in Rm. Inverse homogenization makes use of a Stieltjes analytic representation for the effective complex permittivity, which depends upon R, unlike for the periodic case.
Farhat M, Guenneau S, Chen PY, et al., 2019, Scattering Cancellation-Based Cloaking for the Maxwell-Cattaneo Heat Waves, Physical Review Applied, Vol: 11
We theoretically propose scattering cancellation-based cloaks for heat waves that obey the Maxwell-Cattaneo equation. The proposed cloaks possess carefully tailored diffusivity to cancel the dipole scattering from the object that they surround, and thus can render a small object invisible in the near and far fields, as demonstrated by full-wave finite-element simulations. Mantle heat cloaking is further analyzed and proposed to simplify the design and bring this cloaking technology one step closer to its practical implementation, with promising applications in nanoelectronics and defense-related applications.
Klotz G, Malléjac N, Guenneau S, et al., 2019, Controlling frequency dispersion in electromagnetic invisibility cloaks., Sci Rep, Vol: 9
Electromagnetic cloaking, as challenging as it may be to the physicist and the engineer has become a topical subject over the past decade. Thanks to the transformations optics (TO) invisibility devices are in sight even though quite drastic limitations remain yet to be lifted. The extreme material properties which are deduced from TO can be achieved in practice using dispersive metamaterials. However, the bandwidth over which a metamaterial cloak is efficient is drastically limited. We design and simulate a spherical cloak which takes into account the dispersive nature of relative permittivity and permeability tensors realized by plasma-like metamaterials. This spherical cloak works over a broad frequency-band even though these materials are of a highly dispersive nature. We establish two equations of state that link the eigenvalues of the permittivity and permeability tensors in every spherical cloak regardless of the geometrical transformation. Frequency dispersive properties do not disrupt cloaking as long as the equations of states are satisfied in the metamaterial cloak.
Dubois M, Perchoux J, Vanel AL, et al., 2019, Acoustic flat lensing using an indefinite medium, Physical Review B: Condensed Matter and Materials Physics, Vol: 99, ISSN: 1098-0121
Acoustic flat lensing is achieved here by tuning a phononic array to have indefinite medium behavior in a narrow frequency spectral region along the acoustic branch in the irreducible Brillouin zone (IBZ). This is confirmed by the occurrence of a flat band along an unusual path in the IBZ and by interpreting the intersection point of isofrequency contours on the corresponding isofrequency surface; coherent directive collimated beams are formed whose reflection from the array surfaces create lensing. Theoretical predictions using a mass-spring lattice approximation of the phononic crystal (PC) are corroborated by time-domain experiments, airborne acoustic waves generated by a source with a frequency centered about 10.6 kHz, placed at three different distances from one side of a finite PC slab, constructed from polymeric spheres, yielding distinctive focal spots on the other side. These experiments evaluate the pressure field using optical feedback interferometry and demonstrate precise control of the three-dimensional wave trajectory through a sonic crystal.
Dupont G, Movchan A, Enoch S, et al., 2019, Analysis of low frequency acoustic stop bands in cubic arrays of thick spherical shells with holes, Frontiers in Materials, Vol: 6
We analyse the propagation of airborne pressure waves through a three-dimensional array of rigid coated spheres (shells) in air. When we dig a channel terminated by an air cavity in each rigid shell we observe the appearance of a low frequency stop band. Each shell with a hole acts as a Helmholtz resonator supporting a low frequency localized mode. Isofrequency surfaces and contours reveal the strong anisotropy of the periodic structure at the edge of the stop band. A simple mechanical model of springs and masses allows for asymptotic estimates of the low frequency stop band for elongated channels. Increasing the radius of an air channel shifts up the position, and enlarges, the low frequency stop band. Adding holes in shells also shifts up the frequency of the stop band, and embedded shells lead to additional stop bands. Localization effect induced by a large defect in a periodic macrocell of Helmholtz resonators is finally investigated.
Makwana M, Craster R, Guenneau S, et al., 2019, Exotic symmetry-induced effects in photonic and phononic systems, Pages: 948-949
Predictive theory to geometrically engineer materials in continuum systems to have desired symmetry-induced effects is developed here by bridging the gap between quantum and continuum descriptions. We emphasise a predictive approach, the strength of which is demonstrated by the ability to design well-defined broadband edge states, valley-Hall networks and anisotropic quasicrystalline effects. We solely use semi-analytical models; this means we can concentrate cleanly upon issues such as group theory, and its influence upon the effects we see, without numerical distractions.
Ungureanu B, Brûlé S, Achaoui Y, et al., 2019, Modeling large scale metamaterials for elastic waves control, Pages: 946-947
We’ve studied and proposed to apply the large scale metamaterials properties, which are based on the negative values of the Bulk modules K and G; the Young modulus, of longitudinal elasticity, as well as on the negative mass density, in order to obtain elastic waves control. These negative values are obtained with the help of the local resonance of the elementary cells that lead to very dispersive properties of the metamaterials.
Ungureanu B, Guenneau S, Brule S, et al., 2019, Controlling seismic elastic surface waves via interacting structures, 13th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), Publisher: IEEE, Pages: 438-440
Tang K, Guenneau S, Sebbah P, 2018, Platonic quasicrystal for flatlens focusing of flexural waves, Pages: 373-376
Negative refraction and flat lens focusing of elastic waves has been recently demonstrated experimentally, though restricted to periodic structures where dispersion relations are readily available for prediction and design of superlenses. This is not possible anymore when considering quasiperiodic structures. Here we demonstrate quasicrystal platonic superlensing of elastic waves in perforated metallic thin plates, opening new possibilities for applications of quasi-periodic structures in elastic waves.
Cherkaev E, Guenneau S, Wellander N, 2018, Inverse homogenization of a quasiperiodic composite, Pages: 433-435
The paper deals with inverse homogenization of an electrostatic problem where the geometry on a microscopic scale is given by a quasiperiodic distribution of piecewise constant components defined by the use of a mapping R: n → m , m > n, and a periodic unit cell in m . Inverse homogenization makes use of a Stieltjes analytic representation for the effective complex conductivity, which depends upon R, unlike for the periodic case.
Maurel A, Marigo JJ, Pham K, et al., 2018, Conversion of Love waves in a forest of trees, Physical Review B, Vol: 98, ISSN: 2469-9950
We inspect the propagation of shear polarized surface waves akin to Love waves through a forest of trees of the same height atop a guiding layer on a soil substrate. An asymptotic analysis shows that the forest behaves like an infinitely anisotropic wedge with effective boundary conditions. We discover that the foliage of trees brings a radical change in the nature of the dispersion relation of these surface waves, which behave like spoof plasmons in the limit of a vanishing guiding layer, and like Love waves in the limit of trees with a vanishing height. When we consider a forest with trees of increasing or decreasing height, this hybrid "spoof Love wave" is either trapped within the trees or converted into a downward propagating bulk (shear) wave. These mechanisms of wave trapping and wave conversion appear to be robust with respect to perturbations of height or position of trees in the metawedge and with respect to three-dimensional effects such as regarding a potential change of elastic wave polarization.
Farhat M, Guenneau S, Puvirajesinghe T, et al., 2018, Frequency domain transformation optics for diffusive photon density waves' cloaking., Opt Express, Vol: 26, Pages: 24792-24803
We make use of transformation optics technique to realize cloaking operation in the light diffusive regime, for spherical objects. The cloak requires spatially heterogeneous anisotropic diffusivity, as well as spatially varying speed of light and absorption. Analytic calculations of Photon's fluence confirm minor role of absorption in reduction of far-field scattering, and a monopole fluence field converging to a constant in the static regime in the invisibility region. The latter is in contrast to acoustic and electromagnetic cloaks, for which the field vanishes inside the core. These results are finally discussed in the context of mass diffusion, where cloaking can be achieved with a heterogeneous anisotropic diffusivity.
Craster R, Guenneau S, Hutridurga Ramaiah H, et al., 2018, Cloaking via mapping for the heat equation, Multiscale Modeling and Simulation: A SIAM Interdisciplinary Journal, Vol: 16, Pages: 1146-1174, ISSN: 1540-3459
This paper explores the concept of near-cloaking in the context of time-dependentheat propagation. We show that after the lapse of a certain threshold time, the boundary measure-ments for the homogeneous heat equation are close to the cloaked heat problem in a certain Sobolevspace norm irrespective of the density-conductivity pair in the cloaked region. A regularised trans-formation media theory is employed to arrive at our results. Our proof relies on the study of the longtime behaviour of solutions to the parabolic problems with high contrast in density and conductivitycoefficients. It further relies on the study of boundary measurement estimates in the presence of smalldefects in the context of steady conduction problem. We then present some numerical examples to illustrate our theoretical results.
Puvirajesinghe TM, Zhi ZL, Craster RV, et al., 2018, Tailoring drug release rates in hydrogel-based therapeutic delivery applications using graphene oxide, Journal of the Royal Society Interface, Vol: 15, ISSN: 1742-5662
Graphene oxide (GO) is increasingly used for controlling mass diffusion in hydrogel-based drug delivery applications. On the macro-scale, the density of GO in the hydrogel is a critical parameter for modulating drug release. Here, we investigate the diffusion of a peptide drug through a network of GO membranes and GO-embedded hydrogels, modelled as porous matrices resembling both laminated and 'house of cards' structures. Our experiments use a therapeutic peptide and show a tunable nonlinear dependence of the peptide concentration upon time. We establish models using numerical simulations with a diffusion equation accounting for the photo-thermal degradation of fluorophores and an effective percolation model to simulate the experimental data. The modelling yields an interpretation of the control of drug diffusion through GO membranes, which is extended to the diffusion of the peptide in GO-embedded agarose hydrogels. Varying the density of micron-sized GO flakes allows for fine control of the drug diffusion. We further show that both GO density and size influence the drug release rate. The ability to tune the density of hydrogel-like GO membranes to control drug release rates has exciting implications to offer guidelines for tailoring drug release rates in hydrogel-based therapeutic delivery applications.
Wellander N, Guenneau S, Cherkaev E, 2018, Two-scale cut-and-projection convergence; homogenization of quasiperiodic structures, Pages: 1101-1106, ISSN: 0170-4214
We demonstrate how the problem of finding the effective property of quasiperiodic constitutive relations can be simplified to the periodic homogenization setting by transforming the original quasiperiodic material structure to a periodic heterogeneous material in a higher dimensional space. The characterization of two-scale cut-and-projection convergence limits of partial differential operators is presented. Copyright © 2017 John Wiley & Sons, Ltd.
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